Inspection systems for the analysis of moving web materials have proven critical to modern manufacturing operations. Industries as varied as metal fabrication, paper, non-wovens, and films rely on these inspection systems for both product certification and online process monitoring. They provide value in two major areas. First, they can be used to measure and report product quality in real-time, thereby enabling continuous optimization of the manufacturing process. Second, they are used to identify defective material, enabling that material to be segregated before shipment to the customer. Unfortunately, accurate identification of defective areas can be extremely difficult depending on the nature of the web combined with the time and place of product converting.
Methods of identifying defective regions range from grading rolls using electronic maps to various marking mechanisms. Grading rolls is adequate if one wants to judge bulk statistics of the web. However, in order to remove specific defective regions the roll must be re-inspected. Markers tend to be used to mark only the web edge, and in many cases this is sufficient. Once the mark is identified on the web edge, one usually removes the defective portion. Unfortunately, there are more situations arising where edge marking of webs is not sufficient. These include:
1) Defects difficult to later identify such that even with the presence of an edge mark humans may have a very difficult time finding the defect. Wide webs and small defects compound this situation.
2) Situations where the initial roll is slit into smaller rolls such that the edge mark is no longer present on the narrower rolls.
Besides these difficulties, another concern is raised by the desirability in manufacturing to produce product “just-in-time”. Manufacturing product only when customers require it allows industry to reduce its inventory of finished goods, which results in savings to consumers. However, achieving this goal often has manufacturers working to develop systems and devices that allow a rapid change over between various products.